It is known that a light beam can be significantly distorted as it passes through the atmosphere or an optical system. Distortion of light beams limits the resolution of images received by an optical system for viewing an object. The optical system itself may introduce additional distortions which further reduce the resolution of the image.
Adaptive optical systems for overcoming the above discussed distortions by adding compensators to the optical path when viewing an object are known, e.g. systems described in U.S. Pat. Nos. 4,825,062 and 4,865,454, and 4,950,878.
The systems described in the above cited patents suffer from several drawbacks, i.e.
1) the image must be of an unresolved point source, or
2) the image must be of a relatively simple extended object within a field of view with a uniform background, or
3) the image brightness must be constant during phase sensing operation.
Each of the above referenced sensors require that simple objects be viewed against an uncluttered background, i.e. the sensors will not work with an arbitrary image scene. In particular, none of the above sensors will work with images of scenes which fill the entire sensor field of view, such as a view of the earth from an airplane or satellite.